The terdentate ligand bis-(2-dipheny1phosphinoethyl)amine (I) and the related N-alkyl-substituted ligands where the alkyl group is either methyl (11) or cyclohexyl (111) have been synthesised. Theygive with nickel (11) halides complexes of general formulas NiLX, ( L = I, I1,or 111; X = Br, I), [NiLX],[NiX,] ( L = I or 11; X = CI, Br), and [NiLX]B(C,H5), (L = C ; X = CI, Br, I). With cobalt(l1) halides, complexes of general formula CoLX, ( L = I, 11, or I11 ; X = Br, I ) have beenobtained. The nickel complexes are either low-spin five-co-ordinate or square-planar, depending on the bulkiness of the R group, but in solution they give only square-planar species [NiLX]+. The stereochemistry of the cobalt complexes changes from five-co-ordinate to tetrahedral with increasing bulkiness of the R group. Some similar complexes with the already known bis(diphenylphosphinoethy1) sulphide ligand have a I so been characterized .LOW-SPIN five-co-ordinate complexes of nickel@) and cobalt(11) have been known since 1960,2-4 but it was not until 1965 that high-spin five-co-ordinate complexes of these metals were prepared by adopting sterically suitable ligands and whose donor atoms were fairly electronegative, such as nitrogen and o ~y g e n . ~? ~ Low-spin complexes are formed when the donor atoms are not very electronegative and can form x-bonds, e.g., phosphorus, arsenic, and ~a r b o n . , -~* ~ Sulphur is intermediate.' To investigate the effects of mixing both types of donor atom we studied ' hybrid ' ligands containing all combinations of the donor atoms 0, N, P, As, and S.We now report magnetic, spectrophotometric, conductometric, and molecular-weight measurements of nickel(r1) and cobalt(I1) complexes obtained with the following ligands : bis-(2-diphenylphosphinoethyl) amine (I ; H-PNP) , bis-(2-diphenylphosphinoethyl)methylamine (I1 ; CH,-PNP), bis-(2-diphenylphosphinoethyl)cyclohexylamine (111 ; c-C6H1,-PNP),t and bis-(2-diphenylphosphinoethyl) sulphide (IV ; PSP) . R-N[CH2*CH2*P(C6H5)2]2 (I; R = H) (H-PNP) (11; R = CH,) (CH,-PNP) (111 ; R == C-C&,,) (C-C,H,l-PNP) S[CH2*CH2*P(CGH5)2] (IV) (PSP) A ligand similar to (11), bis-(2-diphenylphosphinoethyl)ethylamine, has been used with Cr and Mo carbonyl complexes,8 and (IV) is known to give a five-co-ordinate complex [Ni( PSP) I,] and some square-planar complexes t c-C,H,, = cyclohexyl.
